where for \(R_{ml}(r)\)  a finite-element discrete variable (FE-DVR) representation
is used with \(m=0\)  and \(m=\pm 1\)  for the \(\Sigma \)  and \(\Pi \)  orbitals, respectively.
The same expansion is used for the \(\chi _c\)  with a range of \(m=-3,\ldots ,3\) , which accounts for two-photon transitions
from the initial \(|m|\le 1\)  states. Photo-electron spectra are computed using tSurff [1]}, [2]}.
Computations were performed with the tRecX code as reported in Ref. [3]}, where the reader can find details on computational implementation and an overview of computational methods.
